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Anatomy of a Small Earthquake Swarm in Southern Ontario, Canada

David W. Eaton
University of Calgary

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
Earthquake swarms are spatio-temporal seismicity clusters that exhibit a gradual rise and fall in seismic moment release, lacking any well-defined mainshock-aftershock sequence (Yamashita 1998). Swarms are common in volcanic regions, where they typically persist for several months or years and generally have maximum event magnitudes of less than 4. Earthquake swarms also occur in nonvolcanic settings and are often classified according to their area of occurrence (Press and Siever 2001). Kurz et al. (2004) have suggested, however, that all tectonic settings may share a common physical generation mechanism for earthquake swarms. Some swarms may be triggered by anthropogenic activities, such as fluid injection or removal (Mereu et al. 1986); this association, in particular, suggests that fluids may play a critical role in swarm seismogenesis.

In the intraplate setting of eastern Canada, earthquake swarms represent one of four distinct categories of characteristic seismic activity, which also include persistent (decades or longer) clusters of seismicity, classic mainshock-aftershock (± foreshock) sequences, and mining-related seismicity (Ma et al. 2008). A small microearthquake swarm (beside Go Home Lake, located at 45.00°N and 79.85°W), herein named the Go Home Lake (GHL) swarm, occurred near Georgian Bay (Canada) during a six-month interval commencing February 2007. The swarm, consisting of 29 detected events with a maximum magnitude of m_N 2.3 (M_w 1.8), reached its peak on February 21. It was preceded on 9 December 2006 by an m_N 2.2 event and was sufficiently well-recorded by a nearby relatively dense distribution of seismic stations, including those deployed as part of the POLARIS project (Eaton et al. 2005) to permit analysis of the seismicity in much greater detail than would otherwise be possible. Given the current interest in long-term underground storage of nuclear waste in this region, . . . [Full Text of this Article]

Department of Earth Sciences
University of Western Ontario
1151 Richmond Street
London, Ontario N6A 5B7 Canada
sma44@uwo.ca
(S. M.)

Department of Geoscience
University of Calgary
Calgary, Alberta T2N 1N4 Canada
eatond@ucalgary.ca
(D. W. E.)